on Mon Feb 09 2009, Andrey Semashev <andrey.semashev-AT-gmail.com> wrote:
My reply may be too late for the discussion, but I'll answer anyway...
David Abrahams wrote:
That's not my concern. My concern is that I don't think lexical_cast is a particularly good interface for its main uses, which could be thought of as "to-string" and "from-string." I disagree. lexical_cast was designed to be simple to use, and I think it does it very well. The "to-string" and "from-string" conversions, in their simple form, are just corner cases.
Eh? What other uses has it got?!
To convert objects of different types between each other.
Yes, I meant what other real-world uses has it got?
I don't know if conversion between types that are not strings is widely used or not.
Then take it from me, it isn't.
Conversions between custom and fundamental floating point types come to mind as an example.
Yes, hypothetically. In reality, no way. Nobody who wrote a custom floating point type would leave its conversion to double up to the vagaries of iostreams, especially ones that hadn't had the right manipulators applied.
I'm quite happy with lexical_cast, except for this default-value issue. Why would I write something new?
Because where you want it to go clearly doesn't mesh with the vision of the original author or the maintainer.
I just don't think lexical_cast is the interface we need for most convenient string conversions. Do you have a better interface in mind?
It would take some thought and discussion to perfect, but just off the top of my head, I'd want something like this:
namespace str { template <class T> struct value { operator T() const; // throws iff parse unsuccessful bool parsed() const; // true iff parse succecssful ... };
template <class String, class T> string::value<T> string::as<T>(String const&);
template <class String, class T> typename enable_if<is_integral<T>, string::value<T> >::type string::as<T>(String const&, unsigned base);
template <class T> std::string to_str(T const& x);
template <class String, class T> String to_str(T const& x); }
This does look pretty much like lexical_cast, a bit extended for string conversions, though.
I'm not against a better support for parsing or formatting in Boost. However, in case of simple needs, I think the potential of lexical_cast is not yet exhausted. Adding another library with so much overlapping functionality may confuse users.
Maybe, but lexical_cast clearly isn't targeted at what some large segment of users needs. -- Dave Abrahams BoostPro Computing http://www.boostpro.com